The present invention relates to subterranean drilling and, in particular, to fluid ejecting nozzles utilized in connection with such drill bits.
In a typical rotary drilling operation, a rotary drill bit is rotated while being advanced into a soil or rock formation. The soil or rock is cut by cutting elements on the drill bit, and these cuttings are flushed to the top of the borehole by the circulation of drilling fluid. The drilling fluid is delivered downwardly through a passage in the drill stem and is ejected outwardly through nozzles threadedly connected in the face of the drill bit. The ejected drilling fluid also cleans and cools the cutting elements.
The nozzles are located proximate the bottom of the borehole and are subjected to the action of abrasive particles moving at high speeds in that region. As a result, the nozzles may eventually be abraded to the point where they fall out or must be replaced. That problem can be alleviated to some extent by forming the nozzle of a hard, wear-resistant material such as cemented tungsten carbide. However, it is difficult to form screw threads in such a hard material. Therefore, it has been proposed to form screw threads in a softer material such as a steel sleeve, and then bond the sleeve to the nozzle body, as disclosed in U.S. Pat. No. 4,381,825 for example. In U.S. Pat. No. 4,542,798 there is disclosed a threaded sleeve which is bonded to a tungsten carbide body to form therewith a locknut which secures a separate nozzle body in place. A shortcoming of the nozzles disclosed in the two above-referenced patents is that they cannot be utilized in connection with nozzles of the orientable type, i.e., the type in which the direction or pattern of the fluid stream can be altered by rotation of the nozzle. Such nozzles are advantageous because it is possible to improve the cleaning and cooling functions (and thus improve the drilling rate) by means of a particular orientation of the fluid streams with respect to the diamond cutting elements.
An orientable nozzle is disclosed in U.S. Pat. No. 4,533,005 wherein the threads are formed in a steel split ring. The ring is mounted on a nozzle body so as to be rotatable relative thereto. The nozzle body and threaded ring include sets of apertures which can receive a wrench. By inserting the wrench into both sets of apertures simultaneously, the threaded sleeve can be rotated and secured in the drill bit body. Afterwards, the wrench can be partially withdrawn so as to engage only the apertures of the nozzle body, thereby enabling the nozzle body to be rotated and reoriented. In this way it is possible to properly direct the direction of the fluid streams. Notwithstanding the advantages of such a nozzle structure, room for improvement remains. For example, it would be desirable to prevent abrasion of the softer sleeve material by particles passing through the apertures of the nozzle body. Also, it would be more desirable if the sleeve were a circumferential continuous member, rather than a split member.